t.w.static.File lies in content-length when byterange falls off the end of the file

New submission from mwh <[email protected]>:

{{{/foo}}} is a 30 byte static resource.  That makes it hard to serve 990 bytes out of it, which is what twisted.web claims it's going to do:

{{{
mwh@grond:Twisted$ telnet localhost 8081
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
GET /foo HTTP/1.1
Host: localhost
Range: bytes=10-1000
Connection: close
 
HTTP/1.1 206 Partial Content
Content-Length: 990
Accept-Ranges: bytes
Content-Range: bytes 10-999/31
Server: TwistedWeb/8.2.0+r26805
Last-Modified: Mon, 04 May 2009 08:40:47 GMT
Connection: close
Date: Mon, 04 May 2009 08:42:26 GMT
Content-Type: text/html

01234567890123456789
^]

telnet> close
}}}

I guess I'll fix this at the same time as I fix #3574.

----------
Type     : defect
Component: web
Keywords : 
Priority : normal
Nosy     : 
----------
http://twistedmatrix.com/trac/ticket/3814